Method, system and apparatus for releasing storage in a fast replication environment

ABSTRACT

Regions of data storage involved with fast replication relationships are managed and tracked in order to maintain the integrity of the data on the source and target volumes. In response to a delete operation referencing specified regions of storage, pending fast replication transfers are completed for source regions, fast replication relationships within the specified regions are withdrawn, and the specified regions of storage are release for subsequent allocation and reuse. The present invention facilitates maintaining synchronization of the storage management components of operating systems with the fast replication mechanisms of storage controllers, and releases unused storage regions for subsequent use. A storage subsystem may receive a delete command and make a determination of whether to release the specified regions of storage according to a state of a fast replication relationship with the regions of storage.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims priority to UnitedStates Utility patent application Ser. No. 10/409,269 entitled “Method,System, and Apparatus for Releasing Storage in a Fast ReplicationEnvironment” and filed on Apr. 8, 2003 for John A. Hulsey, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods, apparatus, and systems for managingstorage sub-systems and networks. Specifically, the invention relates tomethods, apparatus, and systems for managing Fast Replication capablestorage sub-systems and networks.

2. Description of the Related Art

Data processing systems often work with large amounts of data andrequire mechanisms to manage the storage and archiving of that data. Forexample, transaction processing systems typically access large databasesand log results such as transaction records at a very high rate. Theability to quickly and reliably copy data from one storage area toanother enables the deployment of efficient and reliablehigh-performance processing applications and systems.

Fast replication techniques such as IBM's Flashcopy™ technology havebeen developed in response to the need for efficient copying mechanismswithin high-performance processing systems. A fast replication operationgives the appearance of an instantaneous copy, while the actual transferof data is conducted as a background process, or is deferred until thedata to be copied is about to be overwritten. With fast replicationtechniques, applications may conduct data snapshots (point-in-timecopies) and continue processing rather than suspending operation whilethe data transfers occur.

In addition to increased performance, fast replication capable systemssimplify the code complexity of I/O intensive processes such as thoseconducted on large mainframe systems and the like. System performancemay also be increased in that support for fast replication operationsmay be provided by low-level drivers and devices that are optimized forperformance.

Fast replication capable systems preferably support multiple concurrentfast replication data transfers. Since the data transfer may be deferredindefinitely, the act of initiating a fast replication operation betweena source and a target volume is often referred to as “establishing afast replication relationship.” Likewise, canceling a pending fastreplication transfer may be referred to as “withdrawing a fastreplication relationship.”

Without support for fast replication relationships, conducting apoint-in-time copy often requires that a system suspend all tasks thataccess a source and/or target device. Since many systems do not haveexplicit knowledge of the devices that will be accessed by each task,those systems require suspension of all tasks except for the taskconducting the actual fast replication operations. Suspension of thevarious tasks or processes in order to conduct fast replicationoperations greatly reduces the performance of multi-tasking systems.

One challenge of fast replication capable systems, particularly thosesystems capable of establishing multiple simultaneous fast replicationrelationships on a sub-volume basis, is maintaining synchronizationbetween tasks conducting fast replication operations and the memorymanagement or storage management processes of the operating system.Memory involved in a fast replication relationship cannot be safelyallocated to other tasks until the actual data transfer has concluded.As a result, deleting data on fast replication capable storagesubsystems typically requires mechanisms for detecting whether specificregions are involved in a fast replication relationship and whether thedata transfers related to the fast replication relationship haveoccurred. Such means and methods place a heavy burden on the memorymanagement or storage management processes of the operating system andtypically reduce the performance of data processing systems, especiallyin systems where multiple fast replication processes may be occurringsimultaneously.

Therefore, what is needed are methods and apparatus for managing storagethat facilitate reuse of storage regions involved in a fast replicationrelationship and maintain synchronization with the storage managementprocesses of the operating system. Specifically, methods and apparatusare needed that ensure safe withdrawal of any fast replicationrelationships active within specified regions of storage. Such methodsand apparatus would preferably operate at a sub-volume level in a mannerthat is efficient, reliable, and straightforward to implement.

SUMMARY OF THE INVENTION

The methods, apparatus, and systems of the present invention have beendeveloped in response to the present state of the art, and inparticular, in response to the problems and needs in the art that havenot yet been fully solved by currently available fast replication meansand methods. Accordingly, the present invention provides an improvedmethod, apparatus, and system for managing data storage involved in fastreplication operations and relationships.

In accordance with the invention as embodied and broadly describedherein, an improved method, apparatus, and system are presented formanaging fast replication capable data storage. The improved method,apparatus, and system maintain the integrity of storage devices in lightof fast replication operations, release unneeded regions of storage forsubsequent use, and maintain synchronization with storage managementcomponents such as those associated with the operating system of aserver or host.

In one aspect of the invention, a method for managing fast replicationcapable storage includes allocating regions of storage to a task,establishing a fast replication relationship for specified regions ofallocated storage, withdrawing the fast replication relationship for thespecified regions, for example in response to deletion of a file ordataset, and releasing the specified regions of allocated storage forsubsequent use.

The method for managing fast replication capable storage may beconducted in conjunction with a storage management module within asystem utility or operating system and one or more controllers within astorage subsystem. The method may be used with various units of storagesuch as tracks, cylinders, sectors, and blocks.

In certain embodiments, establishing and withdrawing a fast replicationrelationship is accomplished by communicating with one or more storagecontrollers which handle and track fast replication relationships withina storage subsystem. In one embodiment, the communications includeextents that specify a contiguous area of storage via a starting andending index for the starting and ending regions of storage.

In another aspect of the invention, a method for controlling storagedevices includes tracking regions of storage involved in fastreplication relationships, receiving communication referencing specifiedregions to be released for subsequent use, and withdrawing fastreplication relationships for the specified regions. The method may alsoinclude transferring data within the specified regions to a targetdevice previous to withdrawing the fast replication relationships, andinforming a storage management module that the specified regions can bereleased for subsequent use.

In one embodiment, tracking regions of storage involved in fastreplication relationships and withdrawing fast replication relationshipscomprises marking and unmarking regions of storage. Marking andunmarking may be conducted by setting and resetting flags indicatingthat a data transfer is pending for the associated storage region.

In another aspect of the invention, an apparatus for controlling fastreplication capable storage devices, includes a tracking moduleconfigured to track regions involved in a fast replication relationship,and a transfer module configured to transfer data stored within regionsinvolved in a fast replication relationship to a target device. Thetracking module is further configured to withdraw the fast replicationrelationship for specified regions, for example in response tocommunications received from a storage management module executing on aserver or host. The tracking module may also be configured to inform astorage management module that the specified regions can be released forsubsequent use.

In another aspect of the invention, a system for managing fastreplication capable storage includes a storage management moduleexecuting on a server or host that is configured to allocate storage,initiate establishment of fast replication relationships, and initiatewithdrawal of fast replication relationships, and a controllerconfigured to control storage devices, establish fast replicationrelationships for specified regions of storage, and withdraw fastreplication relationships for specified regions of storage as directedby the storage management module. The storage management module may alsobe configured to release the specified regions of storage for subsequentuse. The system for managing fast replication capable storage reducesthe processing burden associated with managing fast replication capablestorage.

The present invention facilitates deleting data within sub-volumestorage regions while maintaining synchronization with the storagemanagement components such as those residing on the host and the fastreplication tracking components such as those residing in a storagesubsystem. In one embodiment maintaining synchronization comprisessending a dataspace delete command to a storage subsystem whichcompletes selected data transfers in order to maintain integrity of thestorage subsystem. In the aforementioned embodiment, data transfersinvolving data regions that are the source of a fast replicationrelationship are completed, while transfers involving data regions thatare the destination of a fast replication relationship are abandoned.

The present invention facilitates relegating tedious housekeeping tasksand data transfers related to fast replication operations to one or morestorage controllers within a storage subsystem. Storage regions may befixed-sized units such as blocks, sectors, cylinders or tracks. Variablelength units such as files or datasets may also be used. These and otherfeatures and advantages of the present invention will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a network system representativeof the environment wherein the present invention may be deployed;

FIG. 2 a is a block diagram illustrating a storage array representativeof the environment wherein the present invention may be deployed;

FIG. 2 b is a block diagram illustrating a fast replication compatiblestorage management system of the present invention;

FIG. 3 is a flow chart illustrating a storage management method of thepresent invention;

FIG. 4 is a flow chart illustrating an establish relationship method ofthe present invention;

FIG. 5 is a flow chart illustrating a withdraw relationship method ofthe present invention; and

FIG. 6 is an illustration depicting a data structure in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a network system 100 is representative of theenvironment wherein the present invention may be deployed. The depictednetwork system 100 includes workstations 110 and servers 120interconnected via a network 130. The network 130 may comprise a localarea network and/or a wide area network.

The depicted network system 100 also includes one or more storage arrays140 interconnected with the servers 120 via a storage network 150. Inone embodiment, the servers 120 are mainframe computers configured toconduct high bandwidth I/O with the storage arrays 140.

FIG. 2 a is a schematic block diagram of a storage sub-system 200illustrating the need of the present invention. The storage sub-system200 is a representative example of sub-systems wherein the presentinvention may be deployed and is one example of the storage array 140depicted in FIG. 1. The storage sub-system 200 includes a storage array210 and one or more controllers 220. In one example, the storage array210 may include a RAID configuration. The storage sub-system 200 mayinclude a plurality of controllers 220 that achieve increasedreliability through redundancy. Additionally, the storage array 210 mayalso achieve increased reliability by interconnecting multiple storagedevices 230 via an array loop 240.

In the depicted embodiment, the storage devices 230 are interconnectedwith an array loop 240. The array loop 240 also interconnects thecontrollers 220 with the storage array 210. The array loop 240circulates communications in both directions to increase reliability andthroughput. In one embodiment, the array loops 240 are point-to-pointloops such as those defined by the fibre channel standard.

In the depicted embodiment, the controllers 220 each support a hostconnection 250. The controllers 220 receive access requests via the hostconnection 250 and service those requests by transferring blocks of datato and from the storage array 210. The blocks of data that aretransferred to the storage array 210 may be redundantly encoded topermit error detection and data recovery in the event of failure of oneof the storage devices 230. Typically, the controllers 220 organize thestorage devices 230 in a redundant manner and present one or morevolumes for use by a one or more servers or hosts such as those depictedin FIG. 1.

In addition to connection and data redundancy, the controllers 220 maysupport various types of fast replication operations. Fast replicationoperations provide the appearance of an instant copy between a sourcevolume and a target volume within a storage sub-system such as thestorage sub-system 200. Fast replication operations conduct datatransfers from the source volume to the target volume at the convenienceof the storage sub-system 200 without halting access to the source ortarget volumes by an external device, such as a host or server.

The challenge of conducting fast replication operations and theirassociated background copies is in maintaining the integrity of thesource and target volumes in light of read, write, and delete operationsto the source and target volumes. Conducting fast replication operationsis particularly challenging if fast replication operations are conductedon a sub-volume level and multiple operations are conductedsimultaneously. The present invention was developed in response to thechallenges of deleting data within fast replication capable storagesub-systems and networks.

Referring to FIG. 2 b, a fast replication compatible storage system 205includes a fast replication capable controller 220, and a server or host120 with a storage management module 280, and one or more storagedevices 230.

The fast replication capable controller 220 facilitates copying datafrom a source device to a target device in a manner that appearsinstantaneous. The controller 220 includes a transfer module 260 thatenables the transfer of data between and within devices, and a trackingmodule 270 that tracks the movement and placement of the data. In oneembodiment, the modules of the controller 220 are software modulesconfigured to conduct their designated tasks.

In one embodiment, the modules of the controller 220 manage data withinfixed-sized regions of storage on the storage devices 230 such assectors, cylinders, or tracks. In certain embodiments, the devices 230managed by the described modules of the controller 220 are logicaldevices or volumes, wherein the data is distributed across multiplephysical devices in a redundant manner.

The transfer module 260 coordinates data transfers between source andtarget devices. In one embodiment, the transfer module 260 conductshandshaking with the storage devices 230 in a manner that validates thereliability of data transfers.

The tracking module 270 tracks the movement and placement of datainvolved in fast replication operations. In one embodiment, the trackingmodule 270 uses bit flags to mark and unmark regions containing datainvolved with fast replication operations. The bit flags enable reliablefast replication operations including fast replication deleteoperations. The operations conducted by the tracking module 270 will bedescribed in more detail in conjunction with FIGS. 4-6.

FIG. 3 is a flow chart illustrating a storage management method 300 ofthe present invention. The storage management method 300 manages storagein a manner that is compatible with conducting fast replicationoperations and may be conducted in conjunction with a storage managersuch as the storage management module 280 and a storage controller suchas the storage controller 220. As depicted, the storage managementmethod 300 includes an allocate storage step 310, an establishrelationship step 320, a withdraw relationship step 330, and a releasestorage step 340.

The allocate storage step 310 allocates memory on a storage device to anapplication or task requiring the memory. The allocated storage may bevirtual memory provided to an application or task that is managed inconjunction with a cache memory residing on a server or host (notshown).

In response to a request by an application, task, system utility or thelike, the establish relationship step 320 establishes a fast replicationrelationship on part or all of the allocated storage. Establishing afast replication relationship facilitates conducting a point-in-timecopy as either a deferred data transfer or a background transferprocess. The allocated storage assigned to a fast replicationrelationship may be the source or destination of a fast replicationrelationship and the associated data transfer.

The established fast replication relationship step 320 and associatedmechanisms maintain the integrity of the source and target volumes ordevices in light of read, and write operations to the allocated storage.Additional details on mechanisms for conducting fast replicationoperations and maintaining fast replication relationships are discussedin conjunction with FIGS. 4-6.

In response to a delete request by an application, task, system utility,or the like, the withdraw relationship step 330 withdraws the fastreplication relationship established in step 320. In certainembodiments, the withdraw relationship step 330 involves sending awithdraw request to one or more storage controllers 220 which determinewhich actions are necessary to fulfill the request. The storagecontrollers 220 in turn, complete the necessary actions and in oneembodiment send an acknowledgment message indicating that the requestedwithdrawal has been completed. One embodiment of the withdrawrelationship step 330 is describe in more detail in conjunction withFIG. 5.

In one embodiment, the withdraw relationship step 330 comprises sendinga dataspace delete command to a storage subsystem 200 which determinesthe state of fast replication relationships involving the target memoryand selectively completes selected data transfers in order to maintainintegrity of the storage subsystem. In the aforementioned embodiment,data transfers involving data regions that are the source of a fastreplication relationship are completed, while transfers involving dataregions that are the destination of a fast replication relationship areabandoned.

Subsequent to the withdraw relationship step 330, the method 300proceeds to the release storage step 340. The release storage step 340releases the storage involved in the fast replication relationship.Releasing the storage involved in the fast replication relationshipfrees the involved storage for subsequent allocation and reuse.

The depicted storage management method 300 facilitates coordinatedmanagement of storage involved in fast replication relationships in astraightforward manner. The elements or steps of the method 300 can bedistributed to run on various storage related components of a dataprocessing system in order to increase system performance androbustness. For example, the withdrawal of a fast replicationrelationship may be conducted by a storage controller or the like thatis in the best position to ascertain the actions necessary to fulfillthe request. The processing burden on the storage management componentsof a host can be reduced and fast replication tracking mechanisms suchas those that execute on a storage controller or the like may besynchronized with the storage allocation mechanisms executing on thehost.

FIG. 4 is a flow chart illustrating an establish relationship method 400in accordance with the present invention. The establish relationshipmethod 400 facilitates conducting multiple fast replication operationson sub-volume regions and may be used to implement the establishrelationship step 320 described in conjunction with FIG. 3. In oneembodiment, the establish relationship method 400 is conducted on thestorage controller 220 in conjunction with the storage management module280 depicted in FIG. 2 b.

The depicted establish relationship method 400 includes a mark regionsstep 410, a background copy test 420, a copy region step 430, an unmarkregion step 440, and a last region test 450. The mark regions step 410designates which regions are earmarked for transfer to the targetvolume.

In one embodiment, the mark regions step 410 comprises setting a copyflag for each region that is designated for transfer to the targetvolume. The copy flags are set to a value indicating a data transferoperation is required for the marked region. In another embodiment, themark regions step 410 comprises initializing a pair of registers whereinone register corresponds to the first region designated for transfer(within a contiguous set of regions) and the other register correspondsto the last region designated for transfer.

The depicted establish relationship method 400 proceeds from the markregions step 410 to the background copy test 420. The background copytest 420 ascertains whether a background copy has been requested, forexample, by the application or utility that invoked the fast replicationcommand. If a background copy has been requested, the method proceeds tothe copy regions step 430. If no background copy has been requested, themethod ends 460.

The copy regions step 430 initiates the transfer of the data within amarked region to a corresponding region on the target volume. In oneembodiment, the source volume and the target volume may be the samevolume. In response to initiating the data transfer, the method 400proceeds to the unmark region step 440.

The unmark region step 440 is conducted to indicate that a data transferis no longer needed. In one embodiment, the unmark region step 440comprises receiving an acknowledgement from the target volume that thedata transfer has occurred, followed by a clearing operation to clearthe copy flag and thereby indicate that a data transfer is no longerrequired. The depicted establish relationship method 400 then proceedsto the last region test 450.

The last region test 450 ascertains whether all of the designatedregions have been transferred to the target volume. In one embodiment,ascertaining comprises checking the copy flags to determine if anytransfers are still required. In another embodiment, such ascertainingcomprises comparing an index for the region just transferred to thetarget volume with a register containing the last region designated fortransfer. If less than all of the designated regions have beentransferred to the target volume, the establish relationship method 400loops to the copy region step 430, otherwise, the method ends 460.

The described establish relationship method 400 is typically conductedby a controller such as the controller 220 in response to receiving afast replication command. For example, in one embodiment an operatingsystem executing on a host invokes the fast replication command via anI/O command block that contains values identifying the source and targetvolumes and extents. The I/O command block is sent to the controller 220in response to a fast replication function call invoked by a systemutility or application.

FIG. 5 is a flow chart illustrating a withdraw relationship method 500of the present invention. The withdraw relationship method 500 is oneexample of the withdraw relationship step 330 depicted in FIG. 3. In oneembodiment, the withdraw relationship method 500 is conducted inresponse to reception of a dataspace delete command from a host.

The withdraw relationship method 500 ensures data integrity on thesource and target volumes of a fast replication relationship whendeleting data within a fast replication capable storage subsystem andfacilitates releasing deleted regions for subsequent use. The withdrawrelationship method 500 may be conducted in conjunction with theestablish relationship method 400 and may use the same mechanisms formarking and unmarking regions.

In one embodiment, the withdraw relationship method 500 progressessequentially through a set of specified regions, checks if each regionhas been copied to the target volume, transfers and unmarks thoseregions which need to be copied, and releases the specified regions forsubsequent use. In one embodiment, the regions are specified by extentsassociated with a file or datatset.

The depicted method 500 includes a region marked test 510, a transferregion step 520, an unmark region step 530, a last region test 540, andan inform storage manager step 550. The region marked test 510ascertains whether a region has been copied, for example, by theestablish relationship method 400, to the target volume. In oneembodiment, ascertaining includes testing whether a copy flag is stillset for the region. If the copy flag is no longer set, the region hasbeen copied to the target volume. If the region has been copied to thetarget volume, the method 500 skips to the last region test 540. If theregion has not been copied, the method 500 proceeds to the transferregion step 520.

If the storage region is the source of a fast replication relationship,the transfer region step 520 transfers the region to the target deviceor volume. Since the depicted method 500 is conducted in response to adelete operation, the transfer region step 520 need not be conducted forstorage regions that are the target of a fast replication relationship.

After the transfer region step 520, the method 500 proceeds to theunmark region step 530. Unmarking the region prevents redundant copyingof the region, for example, by the establish relationship method 400,which, in certain embodiments, may be executing concurrently with thewithdraw relationship method 500. In embodiments with concurrentprocesses that mark and unmark regions, standard concurrent processaccess mechanisms, such as test and set mechanisms, or the like, arepreferably deployed in order to maintain the integrity of branchingdecisions within the concurrent processes.

The last region test 540 ascertains whether all of the regions have beenprocessed. In one embodiment, the last region test 540 comprises testinga looping variable. If additional regions need to be processed, themethod 500 loops to the region marked test 510. If no more regions needto be processed, the method proceeds to the inform storage manager step550.

The inform storage manager step 550 is a step that informs the storagemanager that the fast replication relationship for the specified regionshas been withdrawn and the specified regions may be released forsubsequent reuse. Upon completion of the inform storage manager step550, withdraw relationship method 500 ends 560.

The withdraw relationship method 500 does what is necessary to ensurethat one or more specified storage regions may be release for subsequentuse, for example in response to a delete operation referencing thespecified regions. The method may be conducted by a storage controller,or the like, that is best situated to determine the status of fastreplication operations within a storage subsystem.

FIG. 6 is an illustration depicting a data structure 600 in accordancewith the present invention. The data structure 600 is intended to beexemplary of various embodiments and is shown with a source structure600 a for use with source volumes and a target structure 600 b for usewith target volumes. In situations where the source and target volumesare controlled by the same controller, the elements of the sourcestructure 600 a and the target structure 600 b are preferably combinedinto a single structure wherein redundant elements are eliminated.

As depicted, the data structure 600 includes an extent ID 602, an extentstart 604, an extent end 606, and a marking means 608 comprised of copyflags 609. The extent ID 602 uniquely identifies which extent the datastructure 600 pertains to. The extent start 604 and the extent end 606define the bounds of the extent on the source or target volume.

The marking means 608 provides means for tracking which regions have apending copy operation. In the depicted embodiment, the marking means608 comprises a set of copy flags 609 corresponding to each regionwithin the bounds of the extent start 604 and the extent end 606. In theexample shown, completed copies are indicated with a ‘0’ value andpending copies are indicated with a ‘1’ value. Several of the copy flagsare shown with a dash symbol (‘-’) indicating bits that do notcorrespond to regions within the extent and therefore are not used asflags in the depicted example.

The establish relationship method 400 and the withdraw relationshipmethod 500 may use the data structure 600 to control data transfers andrelease storage regions involved in fast replication operations. Themethods 400 and 500 facilitate conducting read, write, and deleteoperations on a sub-volume level while maintaining data integrity in thepresence of pending fast replication transfers. The methods may beconducted in conjunction with various types of storage devices, forexample rotational storage means such as magnetic and optical storagedevices, or semiconductor storage means such as flash memory, and randomaccess memory. The methods 400 and 500 also enable data relocation inthat fast replication data may be located at different positions orlocations on the source and target devices.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method for managing fast replication-capable storage, the methodcomprising: establishing a fast replication relationship between asource storage containing data to be copied and a corresponding targetstorage where the data is intended to be copied; receiving a commandfrom a server comprising use of a specified storage region wherein thespecified storage region comprises at least a portion of the sourcestorage or the target storage and at least a portion of the data on thesource storage has not been copied to the target storage; copying to thetarget storage data in the source storage that has not been copied tothe target storage when the specified storage region comprises at leasta portion of the source storage and then withdrawing the fastreplication relationship; and withdrawing the fast replicationrelationship when the specified storage region comprises at least aportion of the target storage.
 2. The method of claim 1, wherein thecommand from the server comprises a delete operation.
 3. The method ofclaim 2, wherein the delete operation comprises a dataset delete commandto a storage subsystem.
 4. The method of claim 1, wherein the commandfrom a server comprises a command to establish a second fast replicationrelationship.
 5. The method of claim 1, wherein the source storage,target storage, and specified storage region comprise units selectedfrom the group consisting of tracks, cylinders, sectors, and blocks. 6.A method for controlling storage devices, the method comprising:receiving communication from a storage controller that a source storageis available for use, wherein the source storage comprises part of apreviously established fast replication relationship between the sourcestorage and a corresponding target storage; and sending a command to thestorage controller to use a specified storage region wherein thespecified storage region comprises at least a portion of the sourcestorage or the target storage and at least a portion of the data on thesource storage has not been copied to the target storage, wherein thecommand is sufficient for the storage controller to copy to the targetstorage data in the source storage that has not been copied to thetarget storage when the specified storage region comprises at least aportion of the source storage and then withdraw the fast replicationrelationship; and withdraw the fast replication relationship when thespecified storage region comprises at least a portion of the targetstorage.
 7. The method of claim 6, wherein the command from the servercomprises a delete operation.
 8. The method of claim 6, wherein thecommand from the server comprises a command to establish a second fastreplication relationship.
 9. The method of claim 6, wherein the sourcestorage, target storage, and specified storage region comprise unitsselected from the group consisting of tracks, cylinders, sectors, andblocks.
 10. An apparatus for controlling fast replication capablestorage devices, the apparatus comprising: a transfer module configuredto establish a fast replication relationship between a source storagecontaining data to be copied and a corresponding target storage wherethe data is intended to be copied; a storage controller configured toreceive a command from a server to use a specified storage regionwherein the specified storage region comprises at least a portion of thesource storage or the target storage and at least a portion of the dataon the source storage has not been copied to the target storage; atracking module configured to copy to the target storage data in thesource storage that has not been copied to the target storage when thespecified storage region comprises at least a portion of the sourcestorage and then withdraw the fast replication relationship, and towithdraw the fast replication relationship when the specified storageregion comprises at least a portion of the target storage.
 11. Theapparatus of claim 10, wherein the tracking module is further configuredto inform a storage management module that the specified regions can bereleased for subsequent use.
 12. The apparatus of claim 10, wherein thetransfer module is further configured to initiate a transfer of datastored within the source storage to the target storage.
 13. Theapparatus of claim 10, wherein the server and storage controller arepart of a storage subsystem.
 14. The apparatus of claim 10, wherein thesource storage, target storage, and specified storage region compriseunits selected from the group consisting of tracks, cylinders, sectors,and blocks.
 15. The apparatus of claim 10, wherein the tracking moduleis further configured to withdraw the fast replication relationship forthe specified storage regions in response to a delete operationreferencing the specified storage regions.
 16. A system for controllingfast replication capable storage devices, the system comprising: aserver; a storage controller in communication with the server; at leastone storage device in communication with the storage controller; atransfer module in the storage controller configured to establish a fastreplication relationship between a source storage on a storage devicecontaining data to be copied and a corresponding target storage on astorage device where the data is intended to be copied, and to receive acommand from the server to use a specified storage region on a storagedevice wherein the specified storage region comprises at least a portionof the source storage or the target storage and at least a portion ofthe data on the source storage has not been copied to the targetstorage; and a tracking module in the storage controller configured tocopy to the target storage data in the source storage that has not beencopied to the target storage when the specified storage region comprisesat least a portion of the source storage and then withdraw the fastreplication relationship, and to withdraw the fast replicationrelationship when the specified storage region comprises at least aportion of the target storage.
 17. The system of claim 16, wherein thesource storage, target storage, and specified storage region compriseunits selected from the group consisting of tracks, cylinders, sectors,and blocks.
 18. The system of claim 16, wherein the storage controllersynchronizes data storage for a plurality of fast replicationrelationships.